Cutting inserts are used in various cutting tools for the machining of workpieces, particularly metallic workpieces. Indexable cutting inserts, formed from material such as sintered carbides or ceramics, are often used in milling operations, such as machining aluminum, cast iron, steel, stainless steel, nickel-based alloys, cobalt alloys, and titanium. Examples of cutting tools that employ inserts in performing milling operations include face mills, end mills, slotters, and lathes.
In some conventional cutting tools, indexable cutting inserts are removably secured in insert seats disposed within pockets and spaced circumferentially around the outer periphery of a tool body. Conventional inserts may have a cutting edge about the outside of the insert, which provides a number of alternately usable cutting edges. In some cutting tools, a polygonal insert has been employed to make effective use of its corners.
Ordinarily, during a cutting operation, only a portion of the cutting edge actually cuts the workpiece. When one cutting position becomes worn, the insert may be “indexed,” or repositioned, in the seat in order to bring a fresh cutting edge into the active cutting position. When all of the cutting positions are worn, the insert is discarded and replaced with a new one. In such conventional cutting tools, inserts are generally indexed by rotating them in their respective insert seats about an axis defined by the retainer hole to expose a different cutting edge.
The tool body of a conventional cutting tool often has a circular working end and a plurality of pockets, and chip gullets, positioned about the outside circumference of the working end, and each station contains a seating surface for mounting a cutting insert. An insert seat ordinarily includes one or more seating surfaces for locating, positioning, and orienting the insert in the pocket. One of many methods of retention is a common screw, which passes through a retainer hole in each insert and is threaded into a threaded mounting hole in a seating surface to retain the insert in the pocket. Each chip pocket forms a recess, or indentation, in the tool body located between adjacent insert seats. The chip pockets provide clearance regions for chips cut during the operation of the cutting tool.
A conventional threaded hole is generally perpendicular or slightly angled to the broad top and bottom faces of the insert and to the seating surface supporting the bottom face. During cutting of the workpiece, the inserts commonly experience forces that act to tend to cause the insert to be ejected from the insert pocket. The retainer fastener is the primary means by which the insert is retained in the seat. As a result, the retainer is subject to a shear force that can result in the breaking of the retainer.
In addition, the orientation of the retainer in the insert seat requires the removal of a significant amount of the cutting tool body in front of the insert seat. More specifically, the retainer is oriented approximately perpendicular to the face of the major seating surface, i.e., the seating surface in contact with the bottom face of the insert. As a result, a significant amount of the cutting tool body in front of each major seating surface must be removed to allow the retainer to be screwed in and out of the major seating surface. The removal of this cutting tool body material makes the cross-section smaller, thereby weakening it and shortening its useful life.
In other conventional cutting tools, an indexable cutting insert can be removably secured to a seat on a fixed cutting tool, such as a lathe, and oriented so that cutting edges on the insert project beyond the fixed tool. Most often, the fixed tool is held substantially stationary during machining, while the workpiece rotates about an axis. The fixed cutting insert machines the moving workpiece to remove excess material. Conventional fixed tool inserts commonly have a cutting edge disposed around a periphery of one face of the insert to provide a number of alternately usable cutting edges. During a cutting operation, only a portion of the cutting edge actually cuts the workpiece. When one cutting position becomes worn, the insert is “indexed,” or repositioned, in the seat to position a fresh cutting edge in the active cutting position. For these types of cutting tools, the insert is generally indexed by rotating the insert about an axis commonly defined through the retainer hole formed in the insert to rotate the insert about this axis to expose a different cutting edge on the periphery of the insert.
In most cases, conventional cutting tool inserts for these fixed tool applications have a generally flat shape formed by upper and lower major faces oriented generally parallel to each other. The insert has cutting edges disposed around the periphery of only one of the major faces, such as an upper major face, with side walls that taper inwardly toward a smaller, lower major face. In essence, the conventional insert generally has a truncated V-shaped cross section that is wider near the upper major face and narrower near the lower major face with cutting edges about the periphery of the upper major face.
In the tool body, pocket is formed to receive such inserts. Ordinary tool pockets include side walls inclined outwardly to mate with the inclined insert side walls and a major seating surface to retain the insert. When the cutting tool insert is mounted in the seat, the upper major surface of the insert faces away from the lower tool seating surface so that a portion of the insert cutting edges are positioned to contact the workpiece. However, because the cutting edges of prior inserts extend along the same major face, all cutting edges portions, whether or not positioned for machining, tend to have at least a portion thereof exposed to the environment, which allows the unused cutting edges to risk damage from chips, other debris, or handling.
One of the many methods used to retain the cutting insert within the tool seat is a screw, which passes through the retainer hole in the insert and threaded into a mounting hole in the major seating surface to retain the insert in the seat. Typically, the threaded mounting hole is generally perpendicular to the upper and lower major faces of the insert and to the major seating surface of the tool.